1. Field of the Invention
The present invention relates generally to a radio communication system, and in particular, to an apparatus and method for removing signal interference in a Bluetooth radio device mounted in a mobile terminal.
2. Description of the Related Art
Recently, the radio communication and computer industries have become aware that it is possible to realize a radio device and a radio link at a low cost. Such radio device and radio link enable communication between small, portable communication devices, making it possible to remove complicated connection cables between the communication devices. To this end, active research has been carried out. For example, the so-called “Bluetooth” standard has been defined by Ericsson Co., Sweden. The Bluetooth aims to provide mobility to small, short-range radio communication devices, and utility services to business users. The Bluetooth has defined an optimum technical characteristic for the portable computer and communication devices. In particular, the Bluetooth has been designed to provide low-cost, high-efficiency, high-capacity voice and data networking. In a local (or short-range) radio communication system supporting the Bluetooth standard, voice and data can be exchanged in real time between communication devices such as a mobile phone, a notebook computer and a desktop computer, located within a short distance of less than 10 m, through a radio link. The Bluetooth local radio communication system includes a master for transmitting voice/data, and a plurality of slaves for receiving voice/data. The master can be replaced by one of the slaves, and vice versa. That is, the master and the slaves are changeable according to the subject (device) that transmits the voice/data. The radio link defined by the Bluetooth can guarantee information security and prevent interference between information. In addition, the Bluetooth radio device can be manufactured in the form of a microchip, so that it can be easily mounted in the communication devices. Further, the Bluetooth radio device is designed to operate in the (2.4 GHz) band, a worldwide compatible frequency band. The Bluetooth standard specifies two power levels: a low power level for indoor operation and a high power level for inhouse operation. (In-house is defined as a range corresponding to local distance capable of receiving a service. In general, it means a range capable of being serviced within a house or a building of the company. Additionally, indoor indicates a shorter range than that of the in-house, for example, within a room.) The Bluetooth technology supports both point-to-point connection and point-to-multipoint connection. In the case of the point-to-multipoint connection, each master can communicate with a maximum of 7 slaves.
The Bluetooth radio communication system uses an ISM (Industrial, Scientific, Medical) band of 2.4 to 2.4835 GHz, which can be used without government licensing. Since the ISM band used by the Bluetooth radio communication system is open to the public, the Bluetooth radio communication system should be able to tolerate various unpredictable interferences in the ISM band. In order to resolve the interference problem, the Bluetooth radio communication system adopts a frequency hopping spectrum spreading technique. The Bluetooth radio communication system separately supports a 79 hopping technique and a 23 hopping technique, considering a difference in available frequencies of the respective nations. The 79 hopping technique is adopted by certain nations including the U.S. and South Korea, while the 23 hopping technique is adopted by other nations such as Spain.
FIGS. 1A to 1C illustrate a Bluetooth standard frequency band and its RF channels. Referring to FIG. 1A, the Bluetooth standard frequency band ranges from 2.4 to 2.4835 GHz, and 79 1 MHz-bandwidth channels are allocated in the operating frequency range of 2.4015 to 2.4805 GHz. As a result, each of the 79 channels has a center frequency of f=(2402+k)MHz, where k=0, . . . , 78. Specifically, FIG. 1A illustrates a frequency band of the 79 hopping technique and its RF channels.
FIGS. 1B and 1C illustrate frequency bands of the 23 hopping technique and their RF channels. Specifically, FIG. 1B illustrates a frequency band of the 23 hopping technique adopted by France and its RF channels, wherein 23 1 MHz bandwidth channels are allocated in an operating frequency range of 2.4535 to 2.4765 GHz. As a result, each of the 23 channels has a center frequency of f=(2454+k)MHz, where k=0, . . . , 22. Further, FIG. 1C illustrates a frequency band of the 23 hopping technique adopted by Spain and its RF channels, wherein 23 1 MHz-bandwidth channels are allocated in an operating frequency range of 2.4485 to 2.4715 GHz. As a result, each of the 23 channels has a center frequency of f=(2449+k)MHz, where k=0, . . . , 22.
Meanwhile, in a CDMA (Code Division Multiple Access) mobile terminal mounted with a Bluetooth radio device, a part of a third harmonic component of the CDMA transmission frequency belongs to (or overlaps with) the Bluetooth standard frequency band, thus causing interference during the Bluetooth communication. The CDMA transmission frequency provides 20 FAs Frequency assignments) with a channel gap of 1.23 MHz, and third harmonic components of FA=1 and FA=2 frequencies among the 20 FA frequencies belong to the Bluetooth standard frequency band. The FA=1 transmission frequency is 824.640 MHz and the FA=2 transmission frequency is 825.870 MHz. Therefore, as shown in FIG. 2, the third harmonic of the FA=1 transmission frequency is 2473.92 MHz, and the third harmonic of the FA=2 transmission frequency is 2477.61 MHz.
Therefore, the third harmonic of the FA=1 CDMA transmission frequency interferes with a hopping frequency of 2473, 2474 or 2475 MHz (channel center frequency) of the Bluetooth radio device, while the third harmonic of the FA=2 CDMA transmission frequency interferes with a hopping frequency of 2477 and 2478 MHz of the Bluetooth radio device.